Speaking at the Second International Summit on Human Genome Editing at the University of Hong Kong today, He said that “there is another potential pregnancy”, but that it is still at an early stage.

The Associated Press news agency revealed on Monday that He claims to have edited a number of human embryos using the gene-editing technique CRISPR to make them resistant to HIV. Two were then implanted into a woman’s womb, and she allegedly gave birth to the resulting twin girls this month.

He told the packed audience that he was “proud” of his achievement. He said that the father of the girls – who is HIV positive – had lost hope for life before enrolling in the trial. “[Now the father is] saying ‘I will work hard, earn money and take care of these two daughters’,” He said.

After his talk, He was questioned by summit delegates about why he had conducted the trial in secret without consulting his global peers or authorities in China. He responded that he had run the idea for the trial past at least four experts, including one professor from the US and one from China, but did not name them.

He also said that the university where he works – the Southern University of Science and Technology – was unaware that he had used the research money allocated to him to fund his HIV CRISPR trial. He is currently on unpaid leave at the university.

Speaking at the summit after He, David Baltimore from the California Institute of Technology, said, “I think there has been a failure of self-regulation by the scientific community because of a lack of transparency.”

During his talk, He told the summit that eight couples were initially enrolled in the trial, but one had since dropped out. From the seven remaining couples, 30 embryos have been created, of which 70 per cent have been edited, he says. The trial has now been put on hold “due to the current situation,” He added.

To make the embryos resistant to some strains of HIV, He disabled a gene called CCR5.

One of the main safety concerns over using CRISPR gene editing is that the technique can cause extra, unwanted changes elsewhere in an individual’s DNA. But He told the summit that whole-genome sequencing of the newborns’ cord blood showed that no other parts of the genome have been altered.

However, Greg Neely at the University of Sydney in Australia says it’s impossible to know for sure, because the methods we have for detecting off-target mutations are not yet perfect.

In his talk, He said the twin girls – who he has nicknamed Lulu and Nana – were born “normal and healthy”. They will be monitored for at least 18 years to check for off-target mutations, resistance to HIV, and any unanticipated side-effects.

It’s still unclear whether disabling the CCR5 gene – which is involved in immunity – could make them vulnerable to infectious diseases like West Nile virus, but He said the parents were informed of this risk when they agreed to go ahead with the procedure.

He told the summit he has now submitted the details of the trial to a scientific journal so it can be subject to peer review.